Ultrathin Oxide/Metal/Oxide Trilayer Transparent Conducting\nElectrodes for an All-Transparent Flexible UV Photodetecting Device

Amidst\nthe rapid advancement of flexible and transparent optoelectronic\ndevices, the oxide/metal/oxide (O/M/O) trilayer structure has been\nconsidered to be a potential transparent conducting electrode (TCE)\nbecause of its superior stability and better durability as compared\nto single-layered TCEs or metallic films. In this study, we report\nan ultrathin sputter-deposited SnO<sub>2</sub>/Cu/SnO<sub>2</sub> trilayer\nTCE with excellent electrical and optical properties appropriate for\nflexible and transparent optoelectronic devices. All of the deposited\nTCE films are almost amorphous in nature with an excellent smooth\nsurface texture, as evident from the X-ray diffraction and atomic\nforce microscopy studies. The X-ray photoelectron spectroscopy study\nreveals that Cu remains in the elemental state, sandwiched between\ntwo oxide layers. The lowest resistivity value of 1.59 × 10<sup>–4</sup> Ω·cm along with the highest figure of\nmerit value of around 1.37 × 10<sup>–3</sup> Ω<sup>–1</sup> have been obtained for a 23 nm (10/3/10) trilayer.\nThe enhanced conductivity in the films primarily results from carrier\ninjection from the Cu layer to the oxide layer. A ZnO-based flexible\nand all-transparent ultraviolet photodetecting device on polyethylene\nterephthalate substrates featuring optimized O/M/O (10/3/10) electrodes\nachieves responsivity and detectivity values of 0.33 mA/W and 3.06\n× 10<sup>10</sup> Jones, respectively. The device shows a remarkably\nstable photoresponse under flat as well as various bend conditions.\nTherefore, this study provides potential ways for fabricating high-quality\nO/M/O TCEs across a broader spectrum of flexible and transparent optoelectronic\ndevices.